The present invention relates to the structure of a clean room and a method for fabricating a semiconductor device.
When floating particles present in a region of a clean room where semiconductor devices are fabricated by processing semiconductor wafers are adhered onto the semiconductor wafers, the proportion of defectives increases. Therefore, reduction of floating particles is a significant problem in the fabrication of semiconductor devices.
Accordingly, in a clean room, the externally supplied air is introduced through a particle air filter and the introduced air is set to flow downward.
In accordance with size reduction of semiconductor devices on which complicated integrated circuits are built, it is desired, in a clean room, to remove smaller floating particles and to further reduce the number of floating particles.
For this purpose, it is necessary (1) to increase the number of particle air filters provided in a clean room and (2) to employ a higher performance particle air filter capable of removing smaller floating particles.
However, in employing these methods (1) and (2), it is necessary to construct a new clean room or reconstruct a building including a clean room, which requires disadvantageously high cost.
Furthermore, when the number of particle air filters provided in a clean room is increased, the pressure loss of air flow is increased. In order to attain a desired air flow rate with the pressure loss of the air flow increased, it is necessary to use a high performance fan with a large capacity, which disadvantageously increases the operation cost of the clean room.
In consideration of the aforementioned conventional problems, an object of the invention is improving inter-process yield in semiconductor fabrication by reducing the number of floating particles present in a region where a semiconductor substrate is placed.
The present inventors have examined a method for reducing the number of floating particles with attention given to air flow in a clean room. As a result, it has been found that the rate and direction of the air flow affect the number of floating particles and are in close connection with the inter-process yield.
The present invention was devised on the basis of the findings and is specifically as follows:
The clean room of this invention comprises a first clean region in which a semiconductor substrate to be set in a fabrication system is disposed; and a second clean region adjacent to the first clean region in which an operator is disposed, and a first air flow flowing downward is introduced into the first clean region and a second air flow flowing downward is introduced into the second clean region, and a rate of the first air flow is higher than a rate of the second air flow.
In the clean room of this invention, the rate of the first air flow introduced into the first clean region where the semiconductor substrate is disposed is higher than the rate of the second air flow introduced into the second clean region where the operator is disposed. Therefore, floating particles present in a region where the semiconductor substrate is placed are moved to the vicinity of the floor of the clean room so as to be discharged to the outside of the clean room. As a result, the number of particles adhered onto the surface of the semiconductor substrate can be reduced.
In the clean room, the rate of the first air flow is preferably not less than 1.3 times as high as the rate of the second air flow.
Thus, the number of floating particles present in the region where the semiconductor substrate is placed can be remarkably reduced.
The clean room preferably further comprises partition means disposed between the first clean region and the second clean region for separating the first air flow from the second air flow.
In this manner, the first air flow is minimally affected by the second air flow, so that the rate of the first air flow can be much higher than the rate of the second air flow. Therefore, the number of floating particles present in the region where the semiconductor substrate is placed can be further reduced, resulting in further reducing the number of particles adhered onto the surface of the semiconductor substrate.
In the case where the clean room includes the partition means, an area ratio, to the first clean region, of a first air flow inlet for taking in the first air flow is preferably larger than an area ratio, to the second clean region, of a second air flow inlet for taking in the second air flow.
Thus, even when the power of a fan for supplying the outside air to the first air flow inlet is equal to the power of a fan for supplying the outside air to the second air flow inlet, the rate of the first air flow can be higher than the rate of the second air flow. In other words, without exchanging means for supplying the outside air to the clean room such as a duct or a fan, the rate of the first air flow can be made higher than the rate of the second air flow. Accordingly, the number of floating particles can be reduced without largely reconstructing the clean room.
In the case where the clean room includes the partition means, the partition means preferably has a four-plane structure having an upper opening and a lower opening, and the upper opening has an area larger than the lower opening.
Thus, the first air flow is further minimally affected by the second air flow, so that the rate of the first air flow can be much higher than the rate of the second air flow. Therefore, the number of floating particles present in the region where the semiconductor substrate is placed can be further reduced.
In the case where the clean room includes the partition means, the partition means is preferably disposed with a lower end thereof positioned at a height of 1.2 through 1.8 m above a floor.
Thus, the work efficiency of the operator in dealing with the fabrication system or the semiconductor substrate can be retained without spoiling the effect to reduce the number of floating particles.
In the case where the clean room includes the partition means, the partition means is preferably made from a transparent material.
Thus, the work efficiency of the operator in dealing with the fabrication system or the semiconductor substrate can be retained.
The method for fabricating a semiconductor device of this invention comprises a step of setting a semiconductor substrate in a fabrication system through an operation of an operator in a clean room including a first clean region in which the semiconductor substrate to be set in the fabrication system is disposed and a second clean region adjacent to the first clean region in which the operator is disposed, and a first air flow flowing downward is introduced into the first clean region and a second air flow flowing downward is introduced into the second clean region, and a rate of the first air flow is higher than a rate of the second air flow.
In the method for fabricating a semiconductor device of this invention, since the rate of the first air flow introduced into the first clean region where the semiconductor substrate is disposed is higher than the rate of the second air flow introduced into the second clean region where the operator is disposed, floating particles present in a region where the semiconductor substrate is placed can be moved to the vicinity of the floor of the clean room to be discharged to the outside of the clean room. Therefore, the number of particles adhered onto the surface of the semiconductor substrate can be largely reduced, resulting in improving the inter-process yield of semiconductor devices.
In the method for fabricating a semiconductor device, the rate of the first air flow is preferably not less than 1.3 times as high as the rate of the second air flow.
Thus, the number of floating particles present in the region where the semiconductor substrate is placed can be largely reduced, resulting in largely improving the inter-process yield of semiconductor devices.